The present invention relates to a rubber composition for base tread.
In recent years, the fuel consumption of a vehicle has been conducted by reducing rolling resistance of a tire to suppress heating. Particularly, the reduction of the fuel consumption of the vehicle has been strongly required, and excellent low heat build-up properties have been required for a tread having a high occupancy ratio in the tire among tire members.
An excellent grip performance has been also required for the tread of the tire in view of safety in vehicle driving. However, since the low fuel consumption property and the grip performance are rebellion performances, the tread has been generally composed of a two-layer structure of a cap tread/a base tread, and a rubber having low heat build-up properties has been generally employed as the base tread. That is, the low fuel consumption property and the grip performance of the tire are compatible by using a rubber composition having high gripping force for a surface part coming into contact with a road surface such as the cap tread, and by using a rubber composition having low heat build-up properties for an inner layer part such as the base tread.
As mentioned above, although the rubber composition having low heat build-up properties is required for the base tread, the present condition is that the rubber composition for base tread having sufficient low heat build-up properties has not been yet obtained.
Although Japanese Unexamined Patent Publication No. 2003-292529 describes a polymer having a specific structure, it does not assume use for the base tread of the tire.
Although Japanese Unexamined Patent Publication No. 109384/1995 describes a rubber composition for base tread containing a star-type solution polymerization rubber, the rubber composition for base tread did not show sufficient low heat build-up properties.